1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus which deposits ink and a treatment liquid on a recording medium in such a manner that ink is caused to react with the treatment liquid to form an image.
2. Description of the Related Art
In an inkjet type of image forming apparatus, an image is formed on a recording medium by depositing ink from nozzles onto a recording medium while a head in which a plurality of nozzles are arranged and a recording medium are moved relatively with respect to each other.
Regarding an image forming apparatus of this kind, technology is known in which a treatment liquid that insolubilizes (aggregates) the coloring material contained in the ink by reacting with the ink is used in order to improve image quality, water resistance, and hardness. By depositing this treatment liquid on the recording medium in combination with the ink, the ink is fixed onto the recording medium.
Japanese Patent Application Publication No. 11-129461 discloses technology relating to a recording method by which a treatment liquid is deposited after a prescribed volume of ink has permeated into the recording medium, thereby causing reaction of the treatment liquid and the ink within a prescribed range of permeation.
Furthermore, Japanese Patent Application Publication No. 2002-337332 discloses technology relating to an inkjet printer where the equal amount of the treatment liquid is applied evenly by two separate actions, in order to resolve the problem of the difference in quality arising when printing is performed bi-directionally, between a case where the ink is deposited after depositing the treatment liquid, and a case where the treatment liquid is deposited after depositing the ink.
Moreover, Japanese Patent Application Publication No. 58-128862 discloses an inkjet recording method by which ink is deposited after depositing a treatment liquid, subsequently treatment liquid is newly deposited. Hence, the fixing properties and the permeability of the ink can be adjusted, and a protective layer is provided.
According to the invention described in Japanese Patent Application Publication No. 11-129461, so-called “ink ejection first” technology is used in which ink is ejected first, and then treatment liquid is ejected; however, since the treatment liquid is deposited after a prescribed volume of the ink deposited on the recording medium has permeated into the recording medium, then there is a possibility in that image deterioration, such as feathering, is liable to occur.
According to the invention described in Japanese Patent Application Publication No. 2002-337332, ink is deposited after treatment liquid is deposited first, and then treatment liquid is deposited again. In addition, Japanese Patent Application Publication No. 2002-337332 states that, regardless of whether a large or small volume of treatment liquid is deposited initially, image deterioration can occur, and hence it is desirable if half of a prescribed quantity of treatment liquid is deposited each time. However, Japanese Patent Application Publication No. 2002-337332 does not describe the volume of treatment liquid with respect to the ink.
If the volume of treatment liquid deposited initially is too large compared to the volume of ink, then although spreading of the ink on the recording medium is suppressed, the coloring material in the ink becomes a floating state in the vicinity of the center of the treatment liquid deposited onto the recording medium, as shown in FIGS. 13A to 13C, and hence the coloring material becomes separated from the recording medium. Therefore, the coloring material in the ink becomes insoluble without making contact with the recording medium, and hence the fixing of the coloring material to the recording medium is insufficient. Consequently, the coloring material becomes an instable state in the treatment liquid, and a possibility arises in that the image formed on the recording medium can be disrupted by external disturbances, such as impacts occurring during conveyance of the recording medium, or the like.
On the other hand, if the volume of treatment liquid deposited initially is too small, then the deposition surface area of the treatment liquid on the recording medium becomes insufficient, as shown in FIGS. 14A to 14C, and if ink is deposited onto the recording medium in this state, then the ink that does not react with the treatment liquid spreads horizontally over the surface of the recording medium, thus giving rise to feathering.
Japanese Patent Application Publication No. 58-128862 makes no mention of the volume of treatment liquid with respect to the ink.